What is better option b.tech +MS from IIIT Hyderabad or B.tech from a local college and M.tech from IIT?

To make things clear the comparisons between - BTech + MS from IIITH and BTech( local college) + Mtech from IIT is like comparing a indian local college to Stanford or other reputed college.

You can't simply get into Btech + MS from IIITH, you need to be topper in IIT JEE mains .Last year cutoff was 271/360, even many students in top IITs have not get that much score in their mains.

Their research teams and labs are best in the country, comparing to IISC and top IITs.

Even if you are concerned about placement scenarios at the end then they have 16 Lpa, comparable to best IITs and far better than new ones.

You can also apply for undergraduate their through other processes mentioned in their websites. Even if you at the end of second year, I would definitely recommend you to apply for IIIT H and you will not regret it, since you seemed to be concerned about your future

If you are already studying in a central university, I think you should complete and go for M.Tech. If I remember correctly they will take students who have completed their second year who will be then required to study the first year courses before joining the regular batch. The minimum time required for the course is 4 years. So in essence you will take 6 years which is what you would do in the normal course. Then I don't know the modalities of leaving a course in the midway since you havent named the institute. Will the cental University allow for that is another question. You will require permission and certificates to that effect.

Rather I would advise, complete your B.Tech from the central university where you are studying then apply for GATE to study at IIT. This way you have plenty of options of institutes and courses. and if you wish to study at IIIT Hyd then you can even appear for PGEE which is the PG entrance. Thats another good option.